I had one that was doing the same thing. Replaced both the clip latch spring and the op-rod spring, but that didn't fix it.
I then took it to Bruce Dow who pulled the bullet guide and mic'd the rounded "nose" on the bullet guide - found that it was worn beyond spec. A brand-new-in-the-wrap bullet guide didn't work right either - caused the action to not eject at all. He then installed a "newer" one showing slight wear and it solved the problem.
To clarify - he used a Garand "timing gauge" to see where the timing was off. With the original worn bullet guide, the timing was off in the "premature ejection" end of the sequence. With a brand-new-in-the-wrap bullet guide, the timing was off in the other direction - it wouldn't release the op rod when a clip was inserted. The bullet guide that worked properly was slightly used, just a little wear showing on the "nose". The way he explained it to me was that a new bullet guide should work well if everything else is new also; however, since the rest of the action also showed wear it actually took a slightly worn bullet guide to get everything working in sync.
See the photo at the bottom of Page 107 in Kuleck & McKee "M1 Garand Assembly Guide" - the proper dimension for the lug on the bullet guide is 0.175" - 0.179".
If the simple fixes as suggested by wakkoss don't solve the problem, try another bullet guide. You can save yourself a bunch of trial-and-error fitting if you have access to a Garand timing gauge.
Good luck!!
PS - if you can lay your hands on a Holbrook "thumbsaver" Device, you will be amazed at how much more civilized your Garand becomes!
http://www.dgrguns.com/5-Holbrook-Device.htmhttp://www.dgrguns.com/0-main-page-accessories.htm
and some rin up hill and down dale, knapping the chucky stanes to pieces wi' hammers, like sae mony road-makers run daft... to see how the warld was made!